The present invention relates to apparatus for remote signaling to a telephone line over available AC power wires. More particularly, the present invention provides apparatus for communicating over AC power wires between a conventional extension telephone and a conventional telephone line.
U.S. Pat. No. 3,949,172 which issued Apr. 6, 1976, entitled Telephone Extension System Utilizing Power Line Carrier Signals, and in which the present co-inventors are also co-inventors, describes a system for doing very much the same thing as the system described in the present application. That patent describes a special extension telephone that is used by the subscriber in a conventional manner, but, is not at all conventional in construction and electrical design. In the patent, the extension telephone includes a hand set with a microphone at one end and an earphone at the other with separate lines from each, the line from the microphone feeding a transmitter and the line to the earphone coming from a receiver. In addition, the special extension telephone includes a separate line for cradle switch signals, dial signals and transfer/hold signals. Clearly, all of this is not in accordance with the construction of a conventional subscriber's extension telephone, such as presently used in great numbers throughout the world and which are frequently used by plugging into a telephone wall jack that is the well known four-prong type wall jack or the relatively newer modular type wall jack. It is an object of the present invention to provide a power line telephone extension system for coupling signals between a conventional telephone line and a conventional extension telephone, so that any of the great many of conventional extension telephones that are available can be used with the system. The only requirement is that the conventional extension telephone operate properly when it is used in the conventional manner such as by plugging into an available telephone wall jack.
Other kinds of signaling between a conventional telephone line and various kinds of transmit-receive devices over available AC power wires are described in U.S. Pat. No. 4,058,678, entitled Remote Signaling to a Telephone Line Using Power Line Carrier Signals, and in which the present co-inventors are also co-inventors. That patent describes a system whereby appliances or other electrical equipment plugged into the AC power wires at a premises can be controlled by an incoming telephone call to the premises. The incoming telephone call feeds coded signals to the telephone at the premises and these signals are coupled to the AC power wires and received at the location of an appliance which is also plugged into the AC power wires. The received signals can, for example, turn the appliance on or off. The same patent describes a system for signalling an alarm from the premises. The alarm signal, for example, from a fire detector in the premises is transmitted over the AC power wires in the premises to the telephone where it initiates operation of the telephone to call a predetermined number and deliver it a pre-recorded message. Clearly, neither of the systems described in that patent both receives and transmits information signals.
It is an object of the present invention to provide a system that is capable of full duplex operation so that the system can simultaneously transmit and receive information signals during the interval of a telephone call.